Ambisonics is a full-sphere surround sound technique: in addition to the horizontal plane, it covers sound sources above and below the listener. Unlike other multichannel surround formats, its transmission channels do not carry speaker signals. Instead, they contain a speaker-independent representation of a sound field called B-format, which is then decoded to the listener's speaker setup. This extra step allows the producer to think in terms of source directions rather than loudspeaker positions, and offers the listener a considerable degree of flexibility as to the layout and number of speakers used for playback.
In ambisonics, an array of virtual loudspeakers surrounding a listener generates a sound field by decoding a sound file encoded in a scheme known as B-format from a sound source that is isotropically recorded. The sound field generated at the array of virtual loudspeakers can reproduce the effect of the sound source from any vantage point relative to the listener. Such decoding can be used in the delivery of audio through headphone speakers in Virtual Reality (VR) systems. Binaurally rendered high-order ambisonics (HOA) refers to the creation of many (e.g., at least 9) virtual loudspeakers which combine to provide a pair of signals to left and right headphone speakers. Frequently, such rendering takes into account the effect of a human auditory system using a set of Head Related Transfer Functions (HRTFs). Performing convolutions on signals from each loudspeaker with the set of HRTFs provides the listener with a faithful reproduction of the sound source.